Disc or Disk?

Optical discs like CDs are spelled with a "c," and other kinds of computer storage media such as floppy disk drives and external hard drives are spelled with a "k."

Although there is some disagreement, Stedman's medical dictionary recommends the spelling "disc" for all medical uses. You can remember that "optical" has a "c" in it and the spelling "disc" for optical drives and biology (like your optic nerve) also are spelled with a "c."